Back to EveryPatent.com
United States Patent |
5,081,355
|
Miyagawa
,   et al.
|
January 14, 1992
|
Radiation image recording and read-out apparatus
Abstract
A radiation image recording and read-out apparatus comprises a belt feed
device for positioning and moving a flexible, endless stimulable phosphor
belt in its longitudinal direction, so that two desired portions of the
stimulable phosphor belt, which have support sides that face each other,
may be positioned for exposure to radiation in such a way that the support
sides are in close, face-to-face contact with each other or are
approximately parallel to and slightly spaced apart from each other. In an
image recording section, radiation carrying image information is
irradiated onto two portions of the stimulable phosphor belt, which have
support sides that face each other and which have been positioned so as to
be exposed to the radiation, and radiation images are thereby stored on
the two portions. In a single image read-out section, the radiation images
are read out from the two portions. The two portions are then erased in an
erasing section. In an operating section, two image signals detected from
the two portions in the image read-out section are added together or
subtracted from each other.
Inventors:
|
Miyagawa; Ichirou (Kanagawa, JP);
Agano; Toshitaka (Kanagawa, JP)
|
Assignee:
|
Fuji Photo Film Co., Ltd. (Kanagawa, JP)
|
Appl. No.:
|
599164 |
Filed:
|
October 17, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
250/582; 250/588; 250/589 |
Intern'l Class: |
G02B 042/02 |
Field of Search: |
250/327.2 B,327.2 C,327.2 D,327.2 H,327.2 J,327.2 K,484.1 B
|
References Cited
U.S. Patent Documents
3444372 | May., 1969 | De Hart | 250/484.
|
4258264 | Mar., 1981 | Kotera et al.
| |
4276473 | Jun., 1981 | Kato et al.
| |
4315318 | Feb., 1982 | Kato et al.
| |
4356398 | Oct., 1982 | Komaki et al.
| |
4387428 | Jun., 1983 | Ishida et al.
| |
4400619 | Aug., 1983 | Kotera et al.
| |
4847499 | Jun., 1989 | Horikawa | 250/327.
|
4849631 | Jul., 1989 | Ono | 250/327.
|
4855598 | Aug., 1989 | Ohgoda et al.
| |
4859849 | Aug., 1989 | Shimura et al.
| |
4864134 | Sep., 1989 | Hosoi et al.
| |
4947043 | Aug., 1990 | Shimura | 250/327.
|
Foreign Patent Documents |
56-11395 | Feb., 1981 | JP.
| |
56-12599 | Feb., 1981 | JP.
| |
Primary Examiner: Hannaher; Constantine
Assistant Examiner: Glick; Edward J.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
We claim:
1. A radiation image recording and read-out apparatus comprising:
i) a flexible, endless stimulable phosphor belt capable of storing a
plurality of radiation images thereon,
ii) a belt feed means for positioning said endless stimulable phosphor belt
and moving and circulating said stimulable phosphor belt in its
longitudinal direction along a circulation path, so that two desired
portions of said stimulable phosphor belt, which have support sides that
face each other, may be positioned for exposure to radiation in such a way
that said support sides are in close, face-to-face contact with each other
or are approximately parallel to and slightly spaced apart from each
other,
iii) an image recording section in which radiation carrying image
information is irradiated onto said two desired portions of said
stimulable phosphor belt, which have support sides that face each other
and which have been positioned so as to be exposed to the radiation, and
radiation images are thereby stored on said two desired portions of said
stimulable phosphor belt,
iv) a single image read-out section, which is located in the vicinity of
said circulation path of said stimulable phosphor belt and in which a
portion of said stimulable phosphor belt, on which a radiation image was
stored, is exposed to stimulating rays, which cause said portion of said
stimulable phosphor belt to emit light in proportion to the amount of
energy stored thereon during its exposure to the radiation, said emitted
light being photoelectrically detected and converted into an image signal
by a photoelectric read-out means,
v) an erasing section in which, before a next radiation image is stored on
said portion of said stimulable phosphor belt after said image signal has
been obtained therefrom in said image read-out section, energy remaining
on said stimulable phosphor belt is erased, and
vi) an operating section in which two image signals detected from said two
desired portions of said stimulable phosphor belt in said image read-out
section are added together.
2. An apparatus as defined in claim 1 wherein a filter for completely
filtering out the radiation is located such that it can be moved into and
out of the space between said two desired portions of said stimulable
phosphor belt, which have support surfaces that face each other and which
have been positioned so as to be exposed to the radiation.
3. An apparatus as defined in claim 1 wherein said stimulating rays are a
laser beam.
4. A radiation image recording and read-out apparatus comprising:
i) a flexible, endless stimulable phosphor belt capable of storing a
plurality of radiation images thereon,
ii) a belt feed means for positioning said endless stimulable phosphor belt
and moving and circulating said stimulable phosphor belt in its
longitudinal direction along a circulation path, so that two desired
portions of said stimulable phosphor belt, which have support sides that
face each other, may be positioned for exposure to radiation in such a way
that said support sides are in close, face-to-face contact with each other
or are approximately parallel to and slightly spaced apart from each
other,
iii) a radiation energy absorbing filter which is located between said two
desired portions of said stimulable phosphor belt, which have support
sides that face each other and which have been positioned so as to be
exposed to the radiation,
iv) an image recording section in which radiation carrying image
information is irradiated onto said two desired portions of said
stimulable phosphor belt, which have support sides that face each other
and which have been positioned so as to be exposed to the radiation, and
radiation images are thereby stored on said two desired portions of said
stimulable phosphor belt,
v) a single image read-out section, which is located in the vicinity of
said circulation path of said stimulable phosphor belt and in which a
portion of said stimulable phosphor belt, on which a radiation image was
stored, is exposed to stimulating rays, which cause said portion of said
stimulable phosphor belt to emit light in proportion to the amount of
energy stored thereon during its exposure to the radiation, said emitted
light being photoelectrically detected and converted into an image signal
by a photoelectric read-out means,
vi) an erasing section in which, before a next radiation image is stored on
said portion of said stimulable phosphor belt after said image signal has
been obtained therefrom in said image read-out section, energy remaining
on said stimulable phosphor belt is erased, and
vii) an operating section in which two image signals detected from said two
desired portions of said stimulable phosphor belt in said image read-out
section are added together.
5. An apparatus as defined in claim 1 wherein a filter for completely
filtering out the radiation is located such that it can be moved into and
out of the space between said two desired portions of said stimulable
phosphor belt, which have support sides that face each other and which
have been positioned so as to be exposed to the radiation.
6. An apparatus as defined in claim 4 wherein said stimulating rays are a
laser beam.
7. A radiation image recording and read-out apparatus comprising:
i) a flexible, endless stimulable phosphor belt composed of a support
material, which serves as a radiation energy absorbing filter, and a
stimulable phosphor layer, which is overlaid on said support material and
which is capable of storing a plurality of radiation images thereon,
ii) a belt feed means for positioning said endless stimulable phosphor belt
and moving and circulating said stimulable phosphor belt in its
longitudinal direction along a circulation path, so that two desired
portions of said stimulable phosphor belt, which have support sides that
face each other, may be positioned for exposure to radiation in such a way
that said support sides are in close, face-to-face contact with each other
or are approximately parallel to and slightly spaced apart from each
other,
iii) an image recording section in which radiation carrying image
information is irradiated onto said two desired portions of said
stimulable phosphor belt, which have support sides that face each other
and which have been positioned so as to be exposed to the radiation, and
radiation images are thereby stored on said two desired portions of said
stimulable phosphor belt,
iv) a single image read-out section, which is located in the vicinity of
said circulation path of said stimulable phosphor belt and in which a
portion of said stimulable phosphor belt, on which a radiation image was
stored, is exposed to stimulating rays, which cause said portion of said
stimulable phosphor belt to emit light in proportion to the amount of
energy stored thereon during its exposure to the radiation, said emitted
light being photoelectrically detected and converted into an image signal
by a photoelectric read-out means,
v) an erasing section in which, before a next radiation image is stored on
said portion of said stimulable phosphor belt after said image signal has
been obtained therefrom in said image read-out section, energy remaining
on said stimulable phosphor belt is erased, and
vi) an operating section in which two image signals detected from said two
desired portions of said stimulable phosphor belt in said image read-out
section are subtracted from each other.
8. An apparatus as defined in claim 7 wherein a filter for completely
filtering out the radiation is located such that it can be moved into and
out of the space between said two desired portions of said stimulable
phosphor belt, which have support sides that face each other and which
have been positioned so as to be exposed to the radiation.
9. An apparatus as defined in claim 7 wherein said stimulating rays are a
laser beam.
10. A radiation image recording and read-out apparatus comprising:
i) a flexible, endless stimulable phosphor belt capable of storing a
plurality of radiation images thereon,
ii) a belt feed means for positioning said endless stimulable phosphor belt
and moving and circulating said stimulable phosphor belt in its
longitudinal direction along a circulation path, so that two desired
portions of said stimulable phosphor belt, which have support sides that
face each other, may be positioned for exposure to radiation in such a way
that said support sides are in close, face-to-face contact with each other
or are approximately parallel to and slightly spaced apart from each
other,
iii) a radiation energy absorbing filter which is capable of being moved
into and out of the space between said two desired portions of said
stimulable phosphor belt, which have support sides that face each other
and which have been positioned so as to be exposed to the radiation,
iv) an image recording section in which radiation carrying image
information is irradiated onto said two desired portions of said
stimulable phosphor belt, which have support sides that face each other
and which have been positioned so as to be exposed to the radiation, and
radiation images are thereby stored on said two desired portions of said
stimulable phosphor belt,
v) a single image read-out section, which is located in the vicinity of
said circulation path of said stimulable phosphor belt and in which a
portion of said stimulable phosphor belt, on which a radiation image was
stored, is exposed to stimulating rays, which cause said portion of said
stimulable phosphor belt to emit light in proportion to the amount of
energy stored thereon during its exposure to the radiation, said emitted
light being photoelectrically detected and converted into an image signal
by a photoelectric read-out means,
vi) an erasing section in which, before a next radiation image is stored on
said portion of said stimulable phosphor belt after said image signal has
been obtained therefrom in said image read-out section, energy remaining
on said stimulable phosphor belt is erased, and
vii) an operating section in which two image signals detected from said two
desired portions of said stimulable phosphor belt in said image read-out
section are added together or subtracted from each other.
11. An apparatus as defined in claim 10 wherein a filter for completely
filtering out the radiation is located such that it can be moved into and
out of the space between said two desired portions of said stimulable
phosphor belt, which have support sides that face each other and which
have been positioned so as to be exposed to the radiation.
12. An apparatus as defined in claim 10 wherein said stimulating rays are a
laser beam.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image recording and read-out
apparatus wherein a radiation image is stored on each of different
portions of a stimulable phosphor sheet, each portion of the stimulable
phosphor sheet is then exposed to stimulating rays, which cause it to emit
light in proportion to the amount of energy stored thereon during its
exposure to radiation, and the emitted light is detected and converted
into an electric image signal representing the whole radiation image. This
invention particularly relates to a radiation image recording and read-out
apparatus wherein an image signal, which represents the whole radiation
image and which has a high signal-to-noise ratio (S/N ratio), is obtained
or an image signal corresponding to a specific structure in a radiation
image, i.e. to only a certain part of the whole radiation image, is
obtained.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to radiation such as X-rays,
.alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays,
they store part of the energy of the radiation. Then, when the phosphor
which has been exposed to the radiation is exposed to stimulating rays
such as visible light, light is emitted by the phosphor in proportion to
the amount of energy which was stored. A phosphor exhibiting such
properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and
4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395,
it has been proposed to use stimulable phosphors in radiation image
recording and reproducing systems. Specifically, a sheet provided with a
layer of the stimulable phosphor (hereinafter referred to as a stimulable
phosphor sheet) is first exposed to radiation, which has passed through an
object, such as a human body. In this manner, a radiation image of the
object is stored on the stimulable phosphor sheet. The stimulable phosphor
sheet, on which the radiation image has been stored, is then scanned with
stimulating rays, which cause it to emit light in proportion to the amount
of energy stored thereon during its exposure to the radiation. The light
emitted by the stimulable phosphor sheet, when it is exposed to the
stimulating rays, is photoelectrically detected and converted into an
electric image signal. The electric image signal is then processed as
desired, and the processed image signal is then used during the
reproduction of a visible image which has good image quality and can serve
as an effective tool, such as the efficient and accurate diagnosis of an
illness. The visible image finally obtained may be reproduced in the form
of a hard copy or may be displayed on a display device, such as a cathode
ray tube (CRT) display device. In the radiation image recording and
reproducing systems, the stimulable phosphor sheet is used to store the
radiation image temporarily so that a final visible image can be
reproduced therefrom on a final recording medium. For the sake of economy,
therefore, it is desirable that the stimulable phosphor sheet be used
repeatedly.
In order that the stimulable phosphor sheets may be reused as described
above, the energy remaining on the stimulable phosphor sheet after it has
been scanned with stimulating rays should be erased. For this purpose, the
stimulable phosphor sheet may be exposed to light or heat as described in,
for example, U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent
Publication No. 56(1981)-12599. The stimulable phosphor sheet may then be
used again for the recording of a radiation image.
Techniques for carrying out superposition processing on radiation images
have heretofore been disclosed in, for example, U.S. Pat. No. 4,356,398.
In general, radiation images are used for diagnoses of illnesses and for
other purposes. When a radiation image is used for such purposes, it is
required that even small differences in the radiation energy absorption
characteristics among structures of an object can be detected accurately
in the radiation image. The extent, to which such differences in the
radiation energy absorption characteristics can be detected in a radiation
image, is referred to as the contrast detection performance or simply as
the detection performance. A radiation image having better detection
performance has better image quality and can serve as a more effective
tool particularly in, the efficient and accurate diagnosis of an illness.
Therefore, in order for the image quality to be improved, it is desirable
that the detection performance of the radiation image may be improved. The
detection performance is adversely affected by various noises.
In radiation image recording systems using stimulable phosphor sheets, it
has been found that the noises described below occur during the step of
recording a radiation image on a stimulable phosphor sheet and reading out
the radiation image therefrom.
(1) A quantum noise of radiation produced by a radiation source.
(2) A noise due to nonuniformity in the distribution of the stimulable
phosphor coated on the stimulable phosphor sheet or in the distribution of
the stimulable phosphor grains on the stimulable phosphor sheet.
(3) A noise from stimulating rays, which cause the stimulable phosphor
sheet to emit light in proportion to the amount of energy stored thereon
during its exposure to radiation.
(4) An electric noise in the means for detecting light emitted by the
stimulable phosphor sheet and converting it into an electric signal.
(5) A noise of light emitted by the stimulable phosphor sheet.
Superposition processing is carried out in order to reduce the aforesaid
noises markedly so that even small differences in the radiation energy
absorption characteristics among structures of an object can be found
accurately in a visible radiation image, which is reproduced finally, i.e.
the detection performance of the radiation image can be improved markedly.
General techniques for superposition processing and its effects are
described below.
A radiation image is stored on each of a plurality of stimulable phosphor
sheets, which have been placed one upon another. Thereafter, an image
read-out operation is carried out for each of the stimulable phosphor
sheets. A plurality of image signals, which have been obtained from the
image read-out operations, are superposed one upon another. In this
manner, various noises described above can be reduced. Specifically, in
general, noises described in (1) through (5) exhibit different
distributions for different radiation images stored on the stimulable
phosphor sheets. When the image signals detected from the stimulable
phosphor sheets are superposed one upon another, the noises can be
averaged. Therefore, the noises become imperceptible in a superposition
image, which is obtained from superposition processing. Specifically, an
image signal having a high S/N ratio is obtained from superposition
processing. More specifically, most of the noises described in (1) through
(5), particularly, the noise described in (1), which is one of dominant
factors among the noises in a radiation image, can be approximated by the
Poisson statistics. In cases where noises can be approximated by the
Poisson statistics and two radiation images yield equivalent levels of
signals S1 and S2 and equivalent levels of noises N1 and N2, the level of
the signal corresponding to a superposition image equals S1+S2. The
superposition image is obtained by carrying out superposition processing
on the two radiation images. The level of noise in the superposition image
becomes equal to .sqroot.N1.sup.2 +N2.sup.2. The S/N ratio is one of the
indexes representing the detection performance of a radiation image. The
S/N ratios of the two radiation images prior to superposition processing
are represented by the formulas S1/N1 and S2/N2. After superposition
processing has been carried out on the two radiation images, the S/N ratio
of the superposition image is represented by the formula
(S1+S2)/.sqroot.N1.sup.2 +N2.sup.2. Therefore, as a result of
superposition processing, the S/N ratio can be improved. When
superposition processing is carried out on image signals representing the
two radiation images, the values of the image signals may be weighted such
that a markedly high S/N ratio can be obtained.
When a visible radiation image is to be reproduced from the image signal
obtained from superposition processing, gradation processing should
preferably be carried out in order to improve the contrast of the image.
In such cases, the contrast of the whole image may be improved.
Alternatively, the contrast may be improved only for specific frequency
components, i.e. frequency response enhancement processing may be carried
out. As another alternative, both the processing for improving the
contrast of the whole image and the frequency response enhancement
processing may be carried out. When the values of a plurality of image
signals are added together or averaged during superposition processing, an
image signal detected from a stimulable phosphor sheet, which is located
closer to the radiation source than the other stimulable phosphor sheets
are, should preferably be weighted with a larger weighting coefficient. In
this manner, a better superposition image can be obtained than when the
values of the respective image signals are merely added or averaged.
Appropriate weighting coefficients vary, depending on the number of the
stimulable phosphor sheets, which are placed one upon another during the
recording of the radiation images, the thicknesses of the stimulable
phosphor sheets, or the like.
By way of example, when superposition processing is to be carried out, two
stimulable phosphor sheets have heretofore been housed in a cassette such
that they overlap one upon the other. Radiation images of an object are
then recorded on the two stimulable phosphor sheets housed in the
cassette. Thereafter, an image read-out operation is carried out on each
of the two stimulable phosphor sheets, and two image signals are thereby
obtained.
Also, techniques for carrying out subtraction processing on radiation
images have heretofore been known. When subtraction processing is to be
carried out, two radiation images recorded under different conditions are
photoelectrically read out, and digital image signals which represent the
radiation images are obtained. The image signal components of the digital
image signals which represent corresponding picture elements in the
radiation images are then subtracted from each other, and a difference
signal is thereby obtained which represents the image of a specific
structure or part of the object represented by the radiation images. With
the subtraction processing method, two digital image signals are
subtracted from each other in order to obtain a difference signal, and the
radiation image of a specific structure can be reproduced from the
difference signal.
Basically, subtraction processing is carried out with either the so-called
temporal (time difference) subtraction processing method or the so-called
energy subtraction processing method. In the former method, in order to
extract the image of a specific structure of an object from the image of
the whole object, the image signal representing a radiation image obtained
without injection of contrast media is subtracted from the image signal
representing a radiation image in which the image of the specific
structure of the object is enhanced by the injection of contrast media. In
the latter method, an object is exposed several times to radiation with
different energy distributions, or the energy distribution of the
radiation, which has passed through an object, is changed after it has
been irradiated onto one of two radiation storage means, after which the
radiation impinges upon the second storage means. In this manner, two
radiation images, in which different images of a specific structure are
embedded, are obtained. Thereafter, the image signals representing the two
radiation images are weighted appropriately, when necessary, and subjected
to a subtraction process in order to extract the image of the specific
structure.
Subtraction processing is extremely effective, particularly for medical
diagnosis, and electronics research has continued to develop improved
subtraction processing methods.
In the aforesaid radiation image recording and reproducing systems
utilizing a stimulable phosphor sheet, the radiation image stored on the
stimulable phosphor sheet is read out directly as an electric image
signal. Therefore, with such radiation image recording and reproducing
systems, the aforesaid subtraction processing can readily be carried out.
In cases where energy subtraction processing is to be carried out,
radiation images may be stored on two stimulable phosphor sheets so that
the parts of the radiation images corresponding to a specific structure
are different in the two radiation images. For this purposes, two-shot
energy subtraction processing may be employed wherein the operation for
recording a radiation image is carried out twice with two kinds of
radiation having different energy distributions. Alternatively, one-shot
energy subtraction processing may be employed wherein, for example, two
stimulable phosphor sheets placed one upon the other are simultaneously
exposed to radiation, which has passed through an object, such that they
are exposed to radiation having different energy distributions.
In order to carry out one-shot energy subtraction processing, the following
methods have been proposed:
(1) A method wherein a filter, which is constituted of a metal or the like
and which absorbs low energy components of radiation, is located between
two stimulable phosphor sheets, and radiation having different energy
distributions is thereby obtained.
(2) A method wherein two stimulable phosphor sheets provided with layers of
different types of stimulable phosphors are utilized so that no filter
need be used and radiation images to be subjected to subtraction
processing can be recorded with a single image recording operation. With
this method, a stimulable phosphor sheet provided with a stimulable
phosphor layer, which absorbs more of the low energy components of the
radiation than the stimulable phosphor layer of the other stimulable
phosphor sheet, is positioned closer to the object (closer to the
radiation source), and the two stimulable phosphor sheets are
simultaneously exposed to radiation. Such a method is disclosed in, for
example, U.S. Pat. No. 4,855,598.
However, in cases where radiation images are recorded on a plurality of
stimulable phosphor sheets, which are placed one upon another, the
stimulable phosphor sheets are housed in a cassette and subjected to the
image recording operation. After the radiation images have been stored on
the stimulable phosphor sheets but before they are read out from the
stimulable phosphor sheets, the stimulable phosphor sheets must be taken
out of the cassette and respectively loaded into new independent
cassettes, so that the image read-out operation can be carried out on each
of the stimulable phosphor sheets. Therefore, troublesome operations and
considerable time are required.
Also, when the plurality of the stimulable phosphor sheets are sequentially
subjected to the image read-out operations, the time taken for the image
read-out operations becomes long.
As described above, though superposition processing and energy subtraction
processing are efficient for diagnoses, the conventional techniques for
superposition processing and energy subtraction processing have the
drawbacks in that troublesome operations and considerable time are
required. Therefore, it has heretofore not always been possible to carry
out superposition processing or energy subtraction processing,
particularly during mass medical examinations, or the like.
Accordingly, in Japanese Patent Application No. 1(1989)-53179, the
applicant has proposed a novel radiation image recording and read-out
apparatus. With the proposed radiation image recording and read-out
apparatus, superposition processing or energy subtraction processing
(specifically, one-shot energy subtraction processing utilizing no
radiation energy converting filter) is carried out with a stimulable
phosphor sheet such that troublesome operations for, for example, taking
out stimulable phosphor sheets from a cassette need not be carried out and
image read-out operations may be carried out quickly.
Specifically, in the proposed radiation image recording and read-out
apparatus, two long strip-shaped, flexible stimulable phosphor sheets are
located in parallel, and radiation images are recorded on the two
stimulable phosphor sheets with a single, simultaneous exposure to
radiation. Also, two independent image read-out sections for reading out
the radiation images stored the stimulable phosphor sheets and two
independent erasing sections for erasing any energy remaining on the
stimulable phosphor sheets are provided for the two stimulable phosphor
sheets, so that the two radiation images may be read out simultaneously.
With the proposed radiation image recording and read-out apparatus, no
cassette is used, and superposition processing or energy subtraction
processing can be carried out quickly and easily. Particularly, the
proposed radiation image recording and read-out apparatus is advantageous
for mass medical examinations, or the like, wherein quick processing is
required.
However, with the proposed radiation image recording and read-out
apparatus, two stimulable phosphor sheets are used. Therefore, two image
read-out sections are necessary for reading out the radiation images from
the two stimulable phosphor sheets. Accordingly, the radiation image
recording and read-out apparatus has the drawbacks in that it becomes
large and complicated.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a radiation image
recording and read-out apparatus which is suitable for practical use and
with which superposition processing or energy subtraction processing
(specifically, one-shot energy subtraction processing) is carried out such
that troublesome operations for, for example, taking out stimulable
phosphor sheets from a cassette need not be carried out.
Another object of the present invention is to provide a radiation image
recording and read-out apparatus which has a single endless stimulable
phosphor belt and only a single image read-out section, and in which
superposition processing or energy subtraction processing is carried out
with a very simple configuration.
The radiation image recording and read-out apparatus in accordance with the
present invention is characterized by having a single flexible, endless
stimulable phosphor belt, which serves as stimulable phosphor sheets. Two
desired portions of the single stimulable phosphor belt, which have
support sides that face each other, are located parallel and close to each
other for exposure to radiation. Thus radiation images are recorded on the
two desired portions with a single, simultaneous exposure to radiation.
Also, the radiation image recording and read-out apparatus in accordance
with the present invention is provided with a single image read-out
section for reading out the radiation images, which have been stored on
the stimulable phosphor belt, and an erasing section for erasing any
energy remaining on the stimulable phosphor belt after a radiation image
has been read out therefrom. In this manner, the radiation image recording
and read-out apparatus in accordance with the present invention is kept
simple.
The radiation image recording and read-out apparatus in accordance with the
present invention may be embodied in various ways such that superposition
processing, one-shot energy subtraction processing, or both the
superposition processing and the energy subtraction processing can be
carried out.
Specifically, in order that the superposition processing can be carried
out, the present invention provides a radiation image recording and
read-out apparatus comprising:
i) a flexible, endless stimulable phosphor belt capable of storing a
plurality of radiation images thereon,
ii) a belt feed means for positioning said endless stimulable phosphor belt
and moving and circulating said stimulable phosphor belt in its
longitudinal direction along a circulation path, so that two desired
portions of said stimulable phosphor belt, which have support sides that
face each other, may be positioned for exposure to radiation in such a way
that the support sides are in close, face-to-face contact with each other
or are approximately parallel to and slightly spaced apart from each
other,
iii) an image recording section in which radiation carrying image
information is irradiated onto two portions of said stimulable phosphor
belt, which have support sides that face each other and which have been
positioned so as to be exposed to the radiation, and radiation images are
thereby stored on said two portions of said stimulable phosphor belt,
iv) a single image read-out section, which is located in the vicinity of
said circulation path of said stimulable phosphor belt and in which a
portion of said stimulable phosphor belt, on which a radiation image was
stored, is exposed to stimulating rays, which cause said portion of said
stimulable phosphor belt to emit light in proportion to the amount of
energy stored thereon during its exposure to the radiation, said emitted
light being photoelectrically detected and converted into an image signal
by a photoelectric read-out means,
v) an erasing section in which, before a next radiation image is stored on
said portion of said stimulable phosphor belt after said image signal has
been obtained therefrom in said image read-out section, energy remaining
on said stimulable phosphor belt is erased, and
vi) an operating section in which two image signals detected from two
portions of said stimulable phosphor belt in said image read-out section
are added together.
In order that one-shot energy subtraction processing can be carried out,
the radiation image recording and read-out apparatus in accordance with
the present invention may be embodied such that, instead of the operating
section being used in which two image signals detected from two portions
of the stimulable phosphor belt in the image read-out section are added
together, an operating section is used in which the two image signals are
subtracted from each other. In such cases, a radiation energy absorbing
filter is located between the two desired portions of the stimulable
phosphor belt, which have support sides that face each other and which are
positioned for exposure to radiation. Alternatively, a support material of
the stimulable phosphor belt may be constituted of a radiation energy
absorbing filter.
In order that both the superposition processing and the one-shot energy
subtraction processing can be carried out, the radiation image recording
and read-out apparatus in accordance with the present invention may be
embodied such that, instead of the operating section being used in which
two image signals detected from two portions of the stimulable phosphor
belt in the image read-out section are added together, an operating
section is used in which both the addition process and the subtraction
process are carried out on two image signals. In such cases, a radiation
energy absorbing filter is moved into and out of the space between the two
desired portions of the stimulable phosphor belt, which face each other
and which are positioned for exposure to radiation.
The term "radiation energy absorbing filter" as used herein means a
radiation energy converting filter which converts the energy distribution
of the radiation passing therethrough, such that radiation having
different energy distributions impinge upon the two portions of the
stimulable phosphor belt located on both sides of the radiation energy
converting filter. The radiation energy absorbing filter does not
completely filter out the radiation.
In order for the two image signals to be added together or subtracted from
each other, an image signal storage means may be used which stores an
image signal detected first from one portion of the stimulable phosphor
belt. The image signal may then be read from the image signal storage
means, and the addition process or the subtraction process may be carried
out on said image signal and a next image signal detected from the other
portion of the stimulable phosphor belt. Alternatively, the two image
signals may be stored in two image signal storage means, and may then be
subjected to the addition process or the subtraction process.
As described above, two desired portions of the stimulable phosphor belt,
which have support sides that face each other, may be positioned for
exposure to radiation in such a way that the supports sides are in close,
face-to-face contact with each other or are approximately parallel to and
slightly spaced apart from each other. For example, during the image
recording operation, two desired portions of the stimulable phosphor belt,
which have support sides that face each other, may be positioned for
exposure to radiation in such a way that the supports sides are in close,
face-to-face contact with each other. Also, when the stimulable phosphor
belt is to be moved, the two portions may be spaced apart from each other.
When a radiation image, which was stored on a portion of the stimulable
phosphor belt, is to read out in the image read-out section, in order that
an image signal having a high S/N ratio may be obtained, stimulating rays
should preferably be irradiated from the same side of the stimulable
phosphor belt as the source of the radiation during the image recording
operation. Also, in cases where energy subtraction processing is to be
carried out, if stimulating rays are irradiated from the same side of the
stimulable phosphor belt as the source of the radiation was during the
image read-out operation, a subtraction image having good image quality
can be obtained from the energy subtraction processing.
This is because, when the radiation carrying image information is
irradiated to the stimulable phosphor belt and a radiation image is stored
thereon, the extent to which the radiation is scattered by the stimulable
phosphor of the stimulable phosphor belt increases as the radiation
advances from the radiation source side of the stimulable phosphor belt in
the direction of the thickness of the stimulable phosphor belt. Therefore,
at points comparatively deep within the stimulable phosphor belt, image
information having comparatively high noise is stored. Also, the amount of
image information stored decreases in the direction of the thickness of
the stimulable phosphor belt.
With the radiation image recording and read-out apparatus in accordance
with the present invention, the endless stimulable phosphor belt is
employed, and only a single image read-out sec ion is used in which
radiation images are read out from portions of the stimulable phosphor
belt, on which the radiation images were stored. Therefore, with the
radiation image recording and read-out apparatus in accordance with the
present invention, superposition processing and energy subtraction
processing can be carried out with a single configuration. As a result, a
radiation image having a high S/N ratio, i.e. good detection performance,
can be obtained easily from superposition processing. Also, a good
radiation image of a specific structure or part of an object can be
obtained easily from energy subtraction processing. Accordingly, the
radiation image recording and read-out apparatus in accordance with the
present invention is advantageous, for example, for preventing wrong
diagnoses from being made and for finding a disease early.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view showing a first embodiment of the radiation
image recording and read-out apparatus in accordance with the present
invention,
FIG. 2 is a block diagram showing a radiation image read-out circuit, a
memory, a signal processing circuit, or the like, in the first embodiment,
FIG. 3 is a schematic side view showing a second embodiment of the
radiation image recording and read-out apparatus in accordance with the
present invention, and
FIG. 4 is a block diagram showing a radiation image read-out circuit, a
memory, a signal processing circuit, or the like, in the second embodiment
.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinbelow be described in further detail with
reference to the accompanying drawings.
FIG. 1 is a schematic side view showing a first embodiment of the radiation
image recording and read-out apparatus in accordance with the present
invention. By way of example, this embodiment carries out superposition
processing.
With reference to FIG. 1, this embodiment is composed of a main body 20 and
a radiation source housing section 30. In a housing 29 of the main body
20, a pulley 22 is located at the upper part, and a pulley 23 is located
at the lower part and in the rear region. The pulleys 22 and 23 are
rotated by a motor 24 in the direction indicated by the arrow A. The
pulleys 22 and 23, rollers 26, 27, and 28, which will be described later,
and the motor 24 constitute a belt feed means. A stimulable phosphor belt
25, which is capable of storing radiation images thereon, is threaded over
the pulleys 22 and 23. The stimulable phosphor belt 25 is constituted of a
flexible support material and a stimulable phosphor layer overlaid on the
flexible support material, and takes on the form of an endless, long
strip. The stimulable phosphor belt 25 is also threaded over the rollers
26, 27, and 28, which are located between the pulleys 22 and 23, and is
moved and circulated in the directions indicated by the arrows. The
stimulable phosphor belt 25 is positioned such that the flexible support
material, which is permeable to radiation, faces inwardly toward the space
defined by the endless belt, and the stimulable phosphor layer faces
outwardly from of the space defined by the endless belt.
Also, the stimulable phosphor belt 25 is positioned such that its portions
25a and 25b facing each other are close and parallel to each other at the
position between the rollers 26 and 27. This position is exposed to
radiation 35, which has passed through an object 34.
An image recording stand 32 is located facing the portions of the
stimulable phosphor belt 25 between the rollers 26 and 27. The aforesaid
radiation source housing section 30 houses therein a radiation source 33,
which may be constituted of an X-ray tube, or the like, and which faces
the image recording stand 32. When radiation images of an object 34 are to
be recorded, the object 34 (in this case, a person) is placed upright so
that it is in contact with the image recording stand 32, and the radiation
source 33 is then activated to produce the radiation 35. The radiation 35
passes through the object 34 and then impinges upon the portion 25a of the
stimulable phosphor belt 25. In this manner, a radiation image of the
object 34 is stored on the portion 25a of the stimulable phosphor belt 25
(specifically, on the portion of the stimulable phosphor layer overlaid on
the stimulable phosphor belt 25). Also, the radiation 35, which has passed
through the portion 25a of the stimulable phosphor belt 25, is irradiated
onto the portion 25b of the stimulable phosphor belt 25, which is located
close to the portion 25a. Therefore, a radiation image of the object 34 is
stored on the portion 25b of the stimulable phosphor belt 25.
As will be clear from the foregoing, in this embodiment, an image recording
section 40 is constituted of the image recording stand 32 and the
radiation source 33. In this embodiment, a grid 91 for eliminating
scattered radiation is provided between the image recording stand 32 and
the portion 25a of the stimulable phosphor belt 25.
The radiation images stored on the portions 25a and 25b of the stimulable
phosphor belt 25 are read out as electric image signals in an image
read-out section 50. The image read-out section 50 comprises a laser beam
source 51, and a light deflector 53, which may be constituted of a
rotating polygon mirror, or the like. The light deflector 53 reflects and
deflects a laser beam 52, which serves as stimulating rays and which is
produced by the laser beam source 51, in the main scanning direction. The
image read-out section 50 is also provided with a scanning lens 54 for
converging the laser beam 52, which has been deflected by the light
deflector 53, into a small spot having a predetermined diameter at every
position to be scanned on the stimulable phosphor belt 25. The read-out
section 50 also includes a motor 24, which serves as a sub-scanning means
and which moves the stimulable phosphor belt 25 in the sub-scanning
direction at a predetermined speed at least during the image read-out
operation. The image read-out section 50 further comprises a long
photomultiplier 55, which serves as a photoelectric read-out means and
which is located such that a light receiving face of the long
photomultiplier 55 extends along a scanning line (main scanning line) of
the laser beam 52 on the stimulable phosphor belt 25, and a long light
guide member 56, which is optically coupled with the light receiving face
of the long photomultiplier 55. Additionally, a filter 57 for preventing
the laser beam 52 from impinging upon the long photomultiplier 55, is
located between the light guide member 56 and the long photomultiplier 55.
The long photomultiplier is described in detail in, for example, U.S. Pat.
No. 4,864,134.
After the radiation images of the object 34 have been stored on the
portions 25a and 25b of the stimulable phosphor belt 25 in the manner
described above, the motor 24 is rotated to move the stimulable phosphor
belt 25 at a predetermined speed in the directions indicated by the
arrows. At this time, an appropriate level of load is given by a known
means to the stimulable phosphor belt 25 so that the stimulable phosphor
belt 25 is always properly tensioned. While the stimulable phosphor belt
25 is moved in the sub-scanning direction by the motor 24, the laser beam
source 51 and the light deflector 53 are activated, and the laser beam 52
scans the portion 25b of the stimulable phosphor belt 25 in the main
scanning direction. When the portion 25b of the stimulable phosphor belt
25 is exposed to the laser beam 52, the portion 25b emits light 58 in
proportion to the amount of energy stored thereon during its exposure to
the radiation 35. The emitted light 58 enters the light guide member 56
and is efficiently detected by the long photomultiplier 55. Simultaneously
with the main scanning of the laser beam 52 carried out in the manner
described above, the stimulable phosphor belt 25 is moved in the
sub-scanning direction as described above. Accordingly, the radiation
image stored on the portion 25b of the stimulable phosphor belt 25 is
two-dimensionally detected. A signal S1 is generated the long
photomultiplier 55 and is fed to a read-out circuit 59.
Thereafter, the radiation image, which was stored on the portion 25a of the
stimulable phosphor belt 25, is read out therefrom. A signal S2 (i.e. the
signal representing the radiation image stored on the portion 25a of the
stimulable phosphor belt 25) is generated by the long photomultiplier 55
in the image read-out section 50 and is also fed to the read-out circuit
59. The signals S1 and S2, which have thus been fed to the read-out
circuit 59, are fed to a memory 82 and then to a signal processing circuit
86. The signal processing circuit 86 processes the signals received from
the memory 82, and the processed signals are then fed to an image
reproducing apparatus 88.
How the signals S1 and S2 are processed in the read-out circuit 59 and
subsequent circuits will hereinbelow be described with reference to FIG.
2. As described above, the signal S1 generated by the long photomultiplier
55 is fed to the read-out circuit 59. In the read-out circuit 59, the
signal S1 is logarithmically amplified by a logarithmic amplifier 80, and
is then digitized by an A/D converter 81 into a digital read-out image
signal logS1. The digital read-out image signal logS1 is temporarily
stored in the memory 82, then read therefrom and sent to a superposition
operating circuit 83 in the signal processing circuit 86. Also, the signal
S2 generated by the long photomultiplier 55 is fed to the read-out circuit
59. In the read-out circuit 59, the signal S2 is logarithmically amplified
by a logarithmic amplifier 84 and is then digitized by an A/D converter 85
into a digital read-out image signal logS2. The digital read-out image
signal logS2 thus obtained is temporarily stored in the memory 82, then
read therefrom and sent to the superposition operating circuit 83 in the
signal processing circuit 86.
The superposition operating circuit 83 weights the image signals logS1 and
logS2 appropriately, and adds the image signal components of the weighted
image signals together which represent corresponding picture elements in
the two radiation images. Thus a digital sum signal Sadd is obtained,
which can be expressed as
Sadd=a.multidot.logS1+b.multidot.logS2
where a and b each denote a weighting coefficient. The sum signal Sadd is
fed into an image processing circuit 87, which carries out image
processing, such as gradation processing or frequency response processing,
on the sum signal Sadd. After being processed, the sum signal Sadd is sent
to an image reproducing apparatus 88 and used during the reproduction of a
visible radiation image. The image reproducing apparatus 88 may be a
display means such as a cathode ray tube (CRT) or a recording apparatus
for carrying out light beam scanning recording on a photosensitive film,
or may be replaced by an apparatus for storing the image signals in an
image file on an optical or magnetic disk.
In this embodiment, the image signals S1 and S2 are logarithmically
amplified by the logarithmic amplifiers 80 and 84. Alternatively, instead
of being logarithmically amplified, the image signals S1 and S2 may be
directly digitized by the A/D converters 81 and 85. The superposing
operations may then be carried out on the digital image signals thus
obtained. In such cases, the superposing operations are carried out with
the formula
Sadd=a'S1+b'.S2
where a' and b' each denote a weighting coefficient. When the weighting
coefficients a and b or the weighting coefficients a' and b' are adjusted
to appropriate values in the course of carrying out the aforesaid
superposing operations, a superposition image having a high S/N ratio,
i.e. good detection performance, can be obtained from the sum signal Sadd.
In the course of carrying out the superposing operations, it is necessary
that the image signal components of the image signals logS1 and logS2 be
added together which represent corresponding picture elements in the two
radiation images. For this purpose, as shown in FIG. 1 by way of example,
a marker 92 may be provided in the vicinity of the object 34, and
corresponding picture elements in the image signals logS1 and logS2 may be
found by utilizing the signal representing the marker 92 as a reference
signal.
Instead of sending the read-out image signals logS1 and logS2 to the
superposition operating circuit 83, an ordinary visible radiation image
may be reproduced from the image signal logS1 or the image signal logS2.
For this purpose, the image signal logS1 and the image signal logS2 may be
stored in an image file on an optical disk, or the like.
Also, in the embodiment described above, the read-out circuit 5 is provided
with the logarithmic amplifiers 80, 84 and the A/D converters 81, 85 for
the signals S1 and S2. Alternatively, both signals S1 and S2 may be fed
into a single logarithmic amplifier and a single A/D converter. The
read-out image signals logS1 and logS2 generated by the A/D converter may
then be fed to the memory 82 with different timings.
Reverting to FIG. 1, after the radiation images have been read out from the
portions 25b and 25a of the stimulable phosphor belt 25 in the manner
described above, the portions 25b and 25a are moved along the pulley 23.
As a result, different portions of the stimulable phosphor belt 25 are
positioned between the roller 28 and the pulley 22 and between the rollers
26 and 27. Therefore, radiation images can be stored on these portions of
the stimulable phosphor belt 25 in the same manner as that described
above. The recording of radiation images is thus carried out approximately
over the overall length of the stimulable phosphor belt 25. At this time,
the portions 25b and 25a of the stimulable phosphor belt 25 pass over an
erasing section 60, which is located in the vicinity of the pulley 23. In
the erasing section 60, any energy remaining on the portions 25b and 25a
of the stimulable phosphor belt 25 after the radiation images have been
read out therefrom is erased. The erasing section 60 is constituted of
erasing light sources 61, 61, which are located on the side of the surface
of the stimulable phosphor belt 25 on which surface the stimulable
phosphor layer is overlaid. The erasing light sources 61, 61 are
constituted of fluorescent lamps, or the like, and mainly produce erasing
light having wavelengths falling within the stimulation wavelength range
of the stimulable phosphor layers on the stimulable phosphor belt 25. The
erasing light sources 61, 61 are turned on when the portions 25b and 25a
of the stimulable phosphor belt 25 move along the pulley 23. As the
portions 25b and 25a of the stimulable phosphor belt 25 are exposed to the
erasing light, any energy remaining on the portions 25b and 25a after the
radiation images have been read out therefrom is released therefrom.
In this manner, the portions 25b and 25a of the stimulable phosphor belt
25, from which any residual energy has been erased to such an extent that
they are reusable for the recording of radiation images, are moved by the
pulleys 22 and 23. Therefore, the image recording and read-out operations
can be repeated on the stimulable phosphor belt 25. As the erasing light
sources 61, 61, tungsten-filament lamps, halogen lamps, infrared ray lamps
or xenon flash lamps as disclosed in U.S. Pat. No. 4,400,619 may be used
as well as the aforesaid fluorescent lamps. The erasing section 60 may
also be constituted of surface light sources such as panels each composed
of light emitting diodes (LED's) arrayed two-dimensionally or
electroluminescence plates (EL plates).
A second embodiment of the radiation image recording and read-out apparatus
in accordance with the present invention will be described hereinbelow
with reference to FIGS. 3 and 4. In FIGS. 3 and 4, similar elements are
numbered with the same reference numerals with respect to FIGS. 1 and 2.
In this embodiment, a radiation energy absorbing filter is used during the
image recording operation, and energy subtraction processing is carried
out. A radiation energy absorbing filter 71 is located between the
portions 25a and 25b of the stimulable phosphor belt 25, which face each
other and which are positioned for exposure to radiation between the
pulley 22 and the roller 28 and between the rollers 26 and 27.
A radiation image is stored with radiation having a high energy level on
the portion 25a of the stimulable phosphor belt 25, which is located in
front of the radiation energy absorbing filter 71. Also, a radiation image
is stored with radiation having a low energy level on the portion 25b of
the stimulable phosphor belt 25, which is located at the rear of the
radiation energy absorbing filter 71. Therefore, an energy subtraction
image can be obtained by subtracting the image signals from each other,
which have been detected from the portions 25a and 25b of the stimulable
phosphor belt 25. Energy subtraction processing is described in detail in,
for example, U.S. Pat. Nos. 4,855,598 and 4,859,849.
The radiation energy absorbing filter 71 may be constituted of a material,
which absorbs part of radiation, for example, a Cu plate.
In this embodiment, as illustrated in FIG. 4, an operating circuit 183 of a
signal processing circuit 186 carries out subtracting operations. The
subtraction operating circuit 183 weights the image signals logS1 and
logS2, and subtracts the image signal components of the weighted image
signals from each other which represent corresponding picture elements in
the two radiation images. Thus a digital difference signal Ssub is
obtained, which can be expressed as
Ssub=a.multidot.logS1-b.multidot.logS2-c
where a and b each denote a weighting coefficient, and c denotes a bias
component. The difference signal Ssub is fed into the image processing
circuit 87 which carries out image processing, such as gradation
processing or frequency response processing, on the difference signal
Ssub. After being processed, the difference signal Ssub is sent to the
image reproducing apparatus 88 and used during the reproduction of a
visible radiation image.
If the weighting coefficients a and b are adjusted to appropriate values in
the course of the aforesaid subtracting operations being carried out,
image signal components representing parts of the object 34 other than the
specific structure are eliminated in the obtained difference signal Ssub.
Therefore, a visible image of the specific structure can be reproduced
from the difference signal Ssub.
In the embodiment of FIG. 3, the radiation energy absorbing filter 71 is
located between the portions 25a and 25b of the stimulable phosphor belt
25, which face each other. Alternatively, in order that no independent
filter need be used, the support material of the stimulable phosphor belt
25 may be constituted of a material capable of serving as the radiation
energy absorbing filter, and a stimulable phosphor layer may be overlaid
on the support material. Specifically, the surface of the stimulable
phosphor belt 25, which faces inwardly toward the space defined by the
endless belt, may be constituted as a filter, and a stimulable phosphor
layer may be overlaid on the surface of the stimulable phosphor belt 25,
which faces outwardly from the space defined by the endless belt. In such
cases, two parts of the support material corresponding to the portions 25a
and 25b of the stimulable phosphor belt 25 serve as radiation energy
absorbing filters. Therefore, no independent filter need be used. Also,
the stimulable phosphor layers at the portions 25a and 25b of the
stimulable phosphor belt 25 can be located closer to each other and, as a
result, a more accurate energy subtraction image can be obtained.
As another alternative, the radiation energy absorbing filter 71 may be
moved into and out of the space between the portions 25a and 25b of the
stimulable phosphor belt 25. Also, the operating section may be
selectively set to an addition process mode or a subtraction process mode.
In such cases, two radiation images can be recorded without the radiation
energy absorbing filter 71 being used, and the addition process can be
carried out on the two radiation images. Also, two radiation images can be
recorded with the radiation energy absorbing filter 71 being used, and the
subtraction process can be carried out on the two radiation images. Such
an embodiment can serve as both the embodiment for the superposition
processing, which is shown in FIG. 1, and the embodiment for the energy
subtraction processing, which is shown in FIG. 3.
As a still further alternative, in lieu of the radiation energy absorbing
filter 71, a filter which completely filters out the radiation (e.g. a Pb
plate) may be moved into the space between the portions 25a and 25b of the
stimulable phosphor belt 25. In such cases, during the image recording
operation, the radiation impinges only upon the portion 25a of the
stimulable phosphor belt 25, which is located in front of the filter.
Therefore, the ordinary recording of a single radiation image or the image
recording for two-shot energy subtraction processing can be carried out.
For this purpose, the filter which completely filters out the radiation
may be provided such that it can be moved into and out of the space
between the portions 25a and 25b of the stimulable phosphor belt 25.
Top